Controlling how master pages occur

I have a form that has two pages with repeating subforms on each.

The first page is portrait and the second page should be landscape.

I want the first page portrait master to repeat as many times as required based on the subforms added.

Then I want the second page master to occur from that point on depending on how many subforms are added.

Is there a way of controlling which master pages occur in this way.

Thanks for any help.